Tobaccos and cigarettes contain a toxic, odorless and colorless substance called carbon monoxide that injures the walls of blood vessels, causing scarring and subsequent blockage of blood flow. Poor transport of blood deprives the injured site of adequate blood and slows down healing. Tissue healing begins with clotting (hardening) of blood around the wound to seal the bleeding.
Carbon monoxide also takes away oxygen from the blood by attaching to hemoglobin first before oxygen does. Hemoglobin in the blood carries oxygen to the tissues. Tissues deprived of oxygen experience cell death.
Also, nicotine is a vasoconstrictor (narrows blood vessels), thus reducing nutritional blood flow to the wound. Nicotine also triggers the release of cholesterol and stored fat, which may lead to fatty plaque buildup inside the blood vessel. And because blood pressure is high from a narrowed blood opening, fats are mobilized in the bloodstream, leading to clogging. Either way, the end result is atherosclerosis (necrosis, or hardening of the arteries). Recent studies show that prolonged exposure to nicotine gives rise to formation of new blood vessels that supply a lifeline to plaques, causing further congestion and loss of blood vessel elasticity.
The chain of events does not stop there. Nicotine also makes blood coagulate (clot), increasing the risk of blood clots blocking a blood vessel (thrombosis). It also suppresses cells that produce collagen (responsible for tissue integrity) and white blood cells of the immune system that fight infection. This explains why smoking increases the risk of gum infection. Wounds in the mouth that do not heal well or quickly are susceptible to infection, resulting in failure of dental treatment, implant or surgery.
What happens here is also the pathogenesis (course of events) of major illnesses like lung diseases, diabetes, stroke and heart disease. Cigarette smoking accounts for nearly 440,000 deaths every year in the United States.